Portable electronic devices are frequently used to track the location of persons and/or assets. Satellite positioning cannot be used inside most buildings, and indoor positioning systems are typically based on strength and/or quality observations of signals sent and/or received by the portable electronic devices. Alternatively or additionally, locally constrained radiation, such as infrared or short-range radio or microwave transmission, can be used to track the devices.
A number of reference documents, which are commonly-owned patent applications incorporated herein by reference, are listed at the end of this description. The reference documents disclose various techniques for estimating or determining a location of a positioning device. One of the reasons for locating a positioning device is send assistance to a user associated with the positioning device in cases wherein the user requests assistance by means of the positioning device. For instance, positioning devices may be provided with means to trigger an alert condition with a quick hand movement. In response to the alert condition, the positioning device sends an alert signal to the positioning system, or via the positioning system to an alert-processing system.
Some issues that are not fully resolved in the past relate to determination of which persons should be instructed to give assistance to the alerting user. Further non-resolved issues relate to determination whether or not the instruction to give assistance was received and acted on by at least one user able to give assistance, and what should be done if the instruction was not received or acted on.